Address interrupt and current status display

ABSTRACT

A signaling system located at a central station sequentially interrogates a plurality of remotely located transponders. Means are provided for interrupting the normal addressing sequence and for interrogating any particular remote station, and for then displaying the current status of such station.

1451 Apr. 23, 1974 lllllll l ABSTRACT 9/1972- La Falce et 12 Claims, 7 Drawing Figures STATUS DISPLAY 7* James T. Odom, Huntsville, Ala. Assignee: Avco Corporation, Huntsville, Ala.

May 10,1973

Appl. No.: 358,862

340/147 R, 340/409, 340/167 A [51] Int. H04q 9/00, (10% 29/00 340/152 T, 147 R, 163, 340/167 A, 167 R, 409

References Cited UNITED STATES PATENTS 9/1968 Benson 340/163 United States Patent Odom [54] ADDRESS INTERRUPT AND CURRENT [75] Inventor:

22 Filed:

[58] Field of Search......

TO ONE-SHOT 2G 60 LATCH 6 2 LATCH SHEET 1 OF 4 MONITORS l4 MONITORS -|4 MONITORS I4 ,I2 ,I2 I ,I2

REMOTE REMOTE REMOTE ST TION STATION STATION CENTRAL STATION 1 ,IS ,IS I l6 DISPLAY DISPLAY DISPLAY RESPONSE ONE-SHOT 32 Afi 1 LATCH 60 I QM LATCH 54 A L LATCH e2 l l GATE 74 S D GATE 5a f. il, l GATE 52 :::::L J-ii:::

INITIATE I FTERRUPT PATENTEII IIPII 23 I974 SHEET 2 []F 4 SEQUENTIAL SEQUENTIAL SEQUENTIAL 'SWITCHING SWITCHING V SWITCHING CIRCUIT CIRCUIT CIRCUIT INTERRUPT CIRCUIT l 3a ,40 I 42 I ADDRESS ADDRESS ADDRESS SELECTOR SELECTOR SELECTOR E ONE-SHOT V ONE-SHOT V ONE-SHOT J; RESPONSE ONE-SHOT OR GATE -24 AND TO REMOTE OSC'LLATOR GATE STATIONS ADDRESS INTERRUPT AND CURRENT STATUS DISPLAY BACKGROUND OF THE INVENTION The invention involves a transponder security system of the type disclosed in US. Pat. No. 3,634,824 and which includes a signaling system having a plurality of remote stations and a central station. The central station has the capability of interrogating the remote stations in sequence, the address of the remote stations.

being time coded into the interrogating pulse transmissions. In a practical system, the time required to transmit 25 separate interrogations requires 39 seconds. This invention provides means for interrupting the normal sequence and interrogating a selected station, displaying the response from the selected station, and then continuing with the normal interrogating sequence.

THE DRAWINGS FIG. 1 is a block diagram showing a transponder system in which the disclosed invention is utilized;

FIG. 2 is a curve showing the nature of the coded transmitted signal;

FIG. 3 is a curve showing the nature of the coded transpondered signal;

FIG. 4 is a block diagram showing the interrupter system utilized in accordance with this invention;

FIG. 5 is a schematic drawing showing certain of the details of the interrupter circuits and the address selector circuits;

FIG. 6 is a series of curves showing the time relationships occurring within the interrupt circuit; and

FIG. 7 is a block diagram showing the processing of the coded transponded signals from the remote stations. 7

The overall system is shown schematically in FIG. 1. A central station 10 sends to the remote station address. Each of the particular remote stations 12 (of which there may be any number within the time capabilities of the system) responds to a particular interrogation by transmitting back to the central station tone pulses of lengths that are determined by the status and changes of status of the respective monitors 14 connected to it. Having received the responses from the remote station, the central station decodes the response, processes the information'and displays it in displays 16 in a mannerdescribed in US. Pat. No. 3,634,824.

The addresses of the remote stations are contained in a fixed frequency signal of the type shown in FIG. 2. As shown, the central station transmits a first fixed frequency signal having a duration TI. This is followed by a space which occurs for a period T2. The space T2 is then followed by another signal of the same fixed fre quency and having a time period T3 which is then followed by a space having a period T4. The address of the remote station is coded into the transmission by varying each of the time periods T1, T2, and T3. The time period T4 is a fixed period during which the remote station transponds. Theoretically the number of addresses may be multiplied by adding additional time periods, all of which may be variable. In a practical system, only the times TL and T2 were variable to provide a combination of 25 addresses.

As indicated in FIG. 1, each of the remote stations may contain a number of monitors. Certain of the monitors may, for example be arranged to detect the opening of a window, the breaking of a window, the walking on a floor, a fire, or the opening of a door. Each of these conditions is given a priority level. As shown in FIG. 3, a remote station transmits a single frequency back to the central station and it will have a duration determined by the highest level alarm that is causing a transmission. The first period t,,, of the transmission occurs at every interrogation to give a positive indication that the transponder is operative. A level 0 priority alarm has a duration t a leveLl priority alarm will have a duration t and so forth, so that the highest level alarm signal will dominate all transponded signals.

When an indication appears at the central station that an alarm is being transmitted by the remote station, it is desirable to interrupt the normal sequence, and re-interrogate the station from which an alarm is indicated and then display or otherwise read out the particular cause of the alarm. The block diagram in 2 FIG. 4 shows schematically how the addresses to the remote stations are sequentially coded and transmitted, and also howthe normal sequence is interrupted.

The system includes a fixed frequency oscillator 20 which transmits a signal to the remote stations whenever its associated AND gate 22 is enabled. The AND gate 22 is enabled only when it receives the output from an OR gate 24 in addition to the output signal from the oscillator 20. q

"To control the output from the OR gate 24, and therefore to permit the introduction of the appropriate addresses for the remote stations; a plurality of oneshots 26, 28, 30, and 32 are connected in series, that is, the one-shots are arranged so that the trailing edge of onetriggers the next. The output of each of the oneshots is a square wave having a duration determined by the time constants which are set in. The one-shot 32, referred to as the response one-shot, has a fixed time constant so that the duration T4 of its output remains fixed. The time constantsof the.one-shots 26, 28, and 30 are alterable, sequentially or manually, andthe durations ofv the outputs from these one-shots determine the time periods T1, T2, and T3 shown in FIG. 2.

Under normal conditions, the time constants of the one-shots 26, 28, and 30 are changed by sequentially and cyclically introducing different values of resistance into their respective R-C circuits. This is accomplished by means of conventional sequential switching circuits 34, 35, and 36. i

The sequential switching circuits 34, 35, and 36 have a number of stages, each one of which sequentially connects a different resistor value into a respective oneshot R-C network through an associated address selector circuit 38, 40, and 42. The update clock for the sequential switching circuit 34 is'th'e output pulse from the response one-shot 32. After the last stage of the switching circuit 34 is activated, the next update pulse resets it to the first stage and updates sequential switching circuit 35. Similarly, the resetting of the sequential switching circuit 35 updates the switching cir cuit 36. This means that if there are five stations in each 1 switching circuit, there is a possibility of having different addresses. In a system as reduced to practice, there were five stages in the circuit 34'and five stages in the circuit 35 and only a single stage in the circuit 36, so that a total of 25 addresses were possible. The particular resistor selected by the switching circuit 34 is connected into the one shot 26 through address selector 38, the resistor selected by the circuit 35 is connected to one-shot 28 through the address selector 40,

and the resistor selected by the switching circuit 36 is connected into the one-shot 30 by the address selector The response one-shot 32 provides the update pulse for the sequential switching circuit 34 through an interrupt circuit 44 hereinafter to be described along with the address selectors 38-42. A particular address is manually set into the address selectors 38, 40, and 42 through address interrupt terminals 46, 48, and 50. The interrupt circuit 44 and the address selectors 38, 40, and 42 are shown in more detail in FIG. 5, to which reference is now made.

The address selectors 38, 40, and 42 are identical so that only selector 38 and its associated switching circuit 34 are described. Each of the address selectors includes an AND gate 52 having one input terminal connected to the resistors Rl-RS selected by its respective sequential switching cirueit 34, 35, and 36 for connection into the R-C network of a selected one-shot. The other terminal of AND gate 52 is connected to the 6 output of a latch 54. Under normal sequential operation the AND gate 52 is enabled by a logical 1 on the 6 output of latch 54, and an output is provided to the associated one-shot through an OR gate 56.

The address selectors each includes a second AND gate 58 having one input connected to the manually selected resistors R6-R10, any one of which may be manually switched into the RC circuit of its associated oneshot. The other input terminal of of the gate 58 is connected to the 6 output terminal of the latch 54. Under normal sequential operating conditions the Q output of latch 54 is at logical 0, and the AND gate 58 is disabled. The latch 54 is a part of the interrupt circuit 44 which also includes latches tit? and 62, each of which has a Q output terminal. Under sequential operating conditions the Q output of all the latches are set to a logical 0, while the 6 output of latch 54 is set to a logical 1. The pulse from the response one-shot 32 is applied to the sequential switching circuit 34 through a delay 64 and through the first terminal of AND gate 66, the other terminal of which is enabled bt the logical 1 appearing at the 6 output of latch 54.

When it is desired to interrupt the sequential updat- 7 ing of the switching circuit 34, an interrupt pulse is generated by the circuit which includes a capacitor C1, resistors R11 and R12, and an interrupt switch 68. The pulse generated by the discharging of capacitor C1 sets the 0 output of latch 60 to a logical 1 condition. The logical l at the Q output of the latch 60 enables AND gate 70 for passing the output pulses from the response one-shot 32 to a capacitor C2 which serves to provide a spike on the trailing edge of the one-shot pulse for setting the Q output of the latch 54 to a logical 1 and for setting its 6 output to a logical 0. The condition of the Q and 6 outputs of latch 54 disables AND gate 52 and enables AND gate 58 so that one of the manually preselected resistors R6-Rl0 is connected through the AND gate 58 and the OR gate 56 to its respective one shot 26. I

The 6 output of latch 54 is also applied through a delay 72 to reset the Q output of latch 60 to a logical 0 and to set the Q output of latch 62 to a logical l. The output from latch 62 is used to enable an AND gate 74 so that the pulse from the response one-shot 32 resets latches 54 and 62 through a capacitor C3, which serve to provide a pulse on the trailing edge of the next response one-shot pulse. The resetting of the latches 54 and 62 returns the central station to its normal addressing sequence beginning again at the point where it was interrupted. The delay 64 is a short time delay which is used for the purpose of preventing the pulse generated by the response one-shot 32 from passing through gate 66 while latch 54 is being set.

The operation of the interrupt and address selector circuits is summarized as follows: Momentary closing of the switch 68 causes the discharge of capacitor C1 to generate a pulse which is used to set the 0 output of latch 60 to a logical l. The 0 output of latch 60 is gated with the pulse from the response one-shot 32 to set the Q output of latch 54 to a logical l and its 6 output to a logical 0. The capacitor C2 assures that the setting and resetting of latch 54 is on the trailing edge of the response one-shot pulse This interrupts the normal addressing sequence of the central station in time for the generation of a manually selected address, and the 6 output of latch 54 is used to prevent the sequential switching circuits from being updated by disabling gate 66.

The Q output of latch 54 is used to enable the manually selected address through gates 58 and 56 while the 6'output of latch 54 disables the normal address line at gate 52. The output at gate 56 represents the manually selected address and is used to control the timing of the one-shot 26.

The 6 output of latch 54 is applied through delay 72 to reset the Q output of latch 60 back to a logical 0 and to set the Q output of latch 62 to a logical l. The 0 output from latch 62 is used to enable the AND gate 74 so that the next pulse from the response one-shot resets latches 54 and 62 on the trailing edge. This means that the normal sequencing circuits have been interrupted for one complete cycle but are then free to return to their normal sequencing.

The timing frequencies for the various latches are shown in FIG. 6. It will be seen that the interrupt occurs during the period T i.e., from the trailing edge of one response one-shot pulse to the trailing edge of a succeeding one response one-shot pulse.

Referring now to FIG. 7, the transponded signals from each selected remote station are applied to a response receiving and decoding circuit which serves to provide a logical l or a logical 0 output on a particular line, depending on the code level transponded by the remote station. Thus, if no signal is received from the selected remote station, a logical 1 would appear on the line labeled missing; otherwise if a signal of a duration t,,,, as shown in FIG. 3 is decoded, a logical 1 would appear on the level 0" line, and so on through the level n" line.

Each of the level lines m through n is connected to a first input terminal of a respective one of a plurality of AND gates 82, 84, 86, and 88. The current status of the received signals from the remote stations is determined by sequentially scanning these AND gates. For this purpose a missing status one-shot 90, triggered on the leading edge of the response one-shot pulse, is used to enable AND gate 82. A non-missing status" one-shot 92, triggered on the trailing edge of the response one-shot pulse plus an additional signal from a status level switching circuit 94 enables AND gate 84. The status levelswitching circuit 94, enabled by the leading edge of the output pulse'of the one-shot 92 and updated from level 0 through level n by means of a system clock 96, sequentially enables AND gates 84, 86,

and 88. The time for generation of the current status output must, of course, occur within one complete cycle of the transmitted and received signals.

The current status appearing at the outputs of the AND gates 82-88 is applied to an output display 98 through an AND gate 100. The AND gate 100 is enabled by an address-comparator 102 which develops an enabling output signal whenever its two inputs, one from the address selectors 38, 40, and 42 and the other manually selected addresses set in at the terminals 104, 106, and 108 are identical. The address-comparator may comprise two logic circuits, one which is set by the outputs of the address selectors 3842, and one which is manually set in at the display. The comparator provides an output when there is coincidence between the logic circuits.

As previously noted in connection with FIGS. 4 and 5, the output from each address selector 38, 40, and 42 is a resistor Rl-RS or a resistor R6-Rl0, depending on whether the sequencing is to be interrupted. Thus, the AND gate 100 is enabled when the address appearing in the address selectors coincides with that set in at the terminals 104, 106, and 108. The display 98 is enabled when the output from an information and coding circuit 110 is applied. The information and coding circuit 110 sets up the timing for current status which is displayed.

it will be apparent to persons skilled in the art that the disclosed system is subject to various modifications and adaptations, all within the scope of the invention. For example, while three address selectors are shown, it is apparent that the system will work with any number, depending on the number of addresses required by the system and the amount of time sharing which is permitted. In certain circumstances only one address selector may be required.

Furthermore, while the system shown utilizes only four alarm levels including a missing level, it is apparent that any number may be used. While reference is made to a practical system having 25 addresses, it will be understood that in the embodiment as reduced to practice, four remote stations at the same address are transponded simultaneously but at different frequencies and that the system has capabilities, not a part of this invention, for separating and processing the information from four transponders simultaneously.

I claim: I

1. In a signaling system having a central station and a plurality of remote stations, said central station having means for sequentially transmitting time coded address signals to each of said remote stations in a preestablished sequence, each of said remote stations transponding to said central station upon receipt of a respective time coded address signal, the combination comprising:

a fixed frequency oscillator having a fixed frequency output;

a gate having an output terminal and first and second input terminals, said fixed frequency output being applied to the first input terminal, said fixed frequency output being coupled to said remote stations through the output terminal of said gate when said gate is enabled, said gate being enabled when an enabling pulse is applied to said second terminal, the duration. of each enabling pulse establishing said time coded address signals;

enabling pulse generating means for sequentially generating enabling pulses of different durations, the output of said enabling pulse generating means being applied to said second terminal;

a first plurality of duration determining means connectable into said enabling pulse generating means for establishing the duration of said enabling pulse;

sequential switching means for sequentially connecting each of said duration determining means into saidenabling pulse generating means for establishing the durations of said enabling pulse in said preestablished sequence;

a second plurality of selectable duration determining means;

means for interrupting said sequential switching means and for substituting one of said selectable duration determining means for transmitting a selected new time coded address signal; and

means after receiving a signal from a remote station transponding to said selected new time coded address signal for continuing the operation of said sequential switching means.

2. The invention as defined in claim 1. wherein said enabling pulse generating means is a one-shot multivibrator.

3. The invention as defined in claim 2 wherein said first and second pluralities of duration determining means are first and second pluralities of resistors, said resistors being connectable into the R-C network of said one-shot multivibrator for establishing the duration of its output pulse.

4. The invention as defined in claim 3 wherein said sequential switching means is an electronic switch having a stage for each of said first plurality of resistors, each of said stages of said switch sequentially establishing one of said connections in response to an update pulse, said switch recycling to the first stage after the last stage is disconnected.

5. The invention as defined in claim 4, and a second one-shot multivibrator for generating an update pulse, the trailing edge of the output of said first one-shot multivibrator triggering said second one-shot multivibrator, said update. pulse being connected to said sequential circuit means for updating said switch.

6. The invention as defined in claim 5 wherein said means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determinging means comprises:

a first normally closed switch for connecting the output from said second'one-shot multivibrator to said sequential switching means for updating said sequential switching means;

a second normally closed switch connecting sequen tially selected ones of said first duration determining means into the R-C network of said first oneshot multivibrator;

a third switch for connecting a selected one of said second plurality of duration determining means, said second switch being normally open;

means for opening said first and second switches and for closing said third switch; and

means for subsequently closing said first and second switches and for opening said third switch.

7. The invention as defined in claim 6 wherein an addressed remote station transponds during the period of said update pulse;

and means during the period of said update pulse for displaying a received signal from a remote station.

8. The invention as defined in claim 7 wherein said means for displaying a received signal includes a gate having an output terminal and first and second input terminals, said first input terminal being supplied with decoded received signals, said second terminal enabling said gate when supplied with a comparator output;

a comparator having first and second inputs, said first input being a manually selected numerically coded address, said second input being supplied with a numerical coded address representing a selected new time coded address signal, the output of said address comparator being applied to said terminal of said gate and enabling said gate when the numerical addresses in said comparator are in coincidence.

9. In a signaling system having a central station and a plurality of remote stations, said central station having means for sequentially transmitting time coded address signals to each of said remote stations in a preestablished sequence, each of said remote stations transponding to said central station upon receipt of a respective time coded address signal, said time coded address comprising the combination including a fixed frequency signal having a duration Tl followed by a space having a duration T2, in turn followed by a fixed frequency signal having a duration T3, durations T1 and T2 being variable in accordance with a program to generate said time coded signals in said pre-established sequence, said duration T3 being constant, the combination comprising:

a fixed frequency oscillator having a fixed frequency output;

a gate having an output terminal and first and second input terminals, said fixed frequency output being applied to said first input terminal, said fixed frequency output being coupled to said remote stations through the output terminal of said gate when said gate is enabled, said gate being enabled when an enabling pulse is applied to said second terminal;

first, second, third and fourth serially connected oneshot multivibrators, the trailing edge of the output pulse of each of said multivibrators triggering a succeeding multivibrator, the trailing edge of the output of said fourth multivibrator triggering said first multivibrator, each of said multivibrators having an R-C network, the duration of the output pulse of each multivibrator being a function of the parameters of a respective R-C network, the parameters of said third and fourth multivibrators being fixed, the parameters of said first and second one-shot multivibrators being sequentially alterable in accordance with said program, the duration of the outputs of said first, second, and third oneshot multivibrators being equal to T1, T2, and T3, respectively, the output of the fourth one-shot multivibrator having a fixed duration T4;

a first plurality of duration determining means connectable into the R-C network of said first one-shot multivibrator for establishing the durations of the output pulses therefrom;

a second plurality of duration determining means connectable into the RC network of said second one-shot multivibrator for selectively reestablishing the durations of the output pulses therefrom;

sequential switching means for sequentially connecting each of said duration determining means of said first and second pluralities into the R-C networks of said first and second one-shot multivibrators in accordance with said program, said sequential switching means being updated by said fourth oneshot multivibrator;

a third and fourth plurality of selectable duration determining means;

means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determining means of each of said third and fourth pluralities for re-establishing a selected new time coded address signal;

means during the generation of the output pulse of said fourth one-shot multivibrator for displaying a received signal from a remote station; and

means after receiving a signal from said remote station transponding to said selected new time coded address signal for continuing the operation of said sequential switching means.

10. The invention as defined in claim 9 wherein said means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determining means comprises;

a first normally closed switch for connecting the output from said second one-shot multivibrator to said sequential switching means for updating said sequential switching means;

a second normally closed switch connecting sequentially selected ones of said first duration determining means into the R-C network of said first oneshot multivibrator;

a third switch for connecting a selected one of said second plurality of duration determining means, said second switch being normally open;

means for opening said first and second switches and for closing said third switch; and

means for subsequently closing said first and second switches and for opening said third switch.

11. The invention as defined in claim 10 wherein an addressed remote station transponds during the period of said update pulse;

and means during the period of said update pulse for displaying a received signal from a remote station.

12. The invention as defined in claim 11 wherein said means for displaying a received signal includes a gate having an output termianl and first and second input terminals, said first input terminal being supplied with decoded received signals, said second terminal enabling said gate when supplied with a comparator outa comparator having first and second inputs, said first input being a manually selected numerically coded address, said second input being supplied with a numerically'coded address representing a selected new time coded address signal, the output of said address comparator being applied to said terminal of said gate and enabling said gate when the numerical addresses in said comparator are in coincidence.

2:23; I UNI' I'ED SKATES PATENT OFFICE CER'IIFICATE 0F CORRECTION Patent No. 7 1, Dated April 23,, 19 74 I Inventor) James T- Odom It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lineq37, after "sends to" insert the remote stations a series of tone pulses which represent Column 3, line 29, delete one occurrence of "of".

. Column 3, line "30, I "'6" should read Q Column 6, line 49, "determinging" should read determining Colwnn 8, line 53, "termianl" should read terminal Signed and sealed this 1st day of October 19 74.

(SEAL) Attestz' McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Cpmmissioner of Patents 

1. In a signaling system having a central station and a plurality of remote stations, said central station having means for sequentially transmitting time coded address signals to each of said remote stations in a pre-established sequence, each of said remote stations transponding to said central station upon receipt of a respective time coded address signal, the combination comprising: a fixed frequency oscillator having a fixed frequency output; a gate having an output terminal and first and second input terminals, said fixed frequency output being applied to the first input terminal, said fixed frequency output being coupled to said remote stations through the output terminal of said gate when said gate is enabled, said gate being enabled when an enabling pulse is applied to said second terminal, the duration of each enabling pulse establishing said time coded address signals; enabling pulse generating means for sequentially generating enabling pulses of different durations, the output of said enabling pulse generating means being applied to said second terminal; a first plurality of duration determining means connectable into said enabling pulse generating means for establishing the duration of said enabling pulse; sequential switching means for sequentially connecting each of said duration determining means into said enabling pulse generating means for establishing the durations of said enabling pulse in said pre-established sequence; a second plurality of selectable duration determining means; means for interrupting said sequential switching means and for substituting one of said selectable duration determining means for transmitting a selected new time coded address signal; and means after receiving a signal from a remote station transponding to said selected new time coded address signal for continuing the operation of said sequential switching means.
 2. The invention as defined in claim 1 wherein said enabling pulse generating means is a one-shot multivibrator.
 3. The invention as defined in claim 2 wherein said first and second pluralities of duration determining means are first and second pluralities of resistors, said resistors being connectable into the R-C network of said one-shot multivibrator for establishing the duration of its output pulse.
 4. The invention as defined in claim 3 wherein said sequential switching means is an electronic switch having a stage for each of said first plurality of resistors, each of said stages of said switch sequentially establishing one of said connections in response to an update pulse, said switch recycling to the first stage after the last stage is disconnected.
 5. The invention as defined in clAim 4, and a second one-shot multivibrator for generating an update pulse, the trailing edge of the output of said first one-shot multivibrator triggering said second one-shot multivibrator, said update pulse being connected to said sequential circuit means for updating said switch.
 6. The invention as defined in claim 5 wherein said means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determinging means comprises: a first normally closed switch for connecting the output from said second one-shot multivibrator to said sequential switching means for updating said sequential switching means; a second normally closed switch connecting sequentially selected ones of said first duration determining means into the R-C network of said first one-shot multivibrator; a third switch for connecting a selected one of said second plurality of duration determining means, said second switch being normally open; means for opening said first and second switches and for closing said third switch; and means for subsequently closing said first and second switches and for opening said third switch.
 7. The invention as defined in claim 6 wherein an addressed remote station transponds during the period of said update pulse; and means during the period of said update pulse for displaying a received signal from a remote station.
 8. The invention as defined in claim 7 wherein said means for displaying a received signal includes a gate having an output terminal and first and second input terminals, said first input terminal being supplied with decoded received signals, said second terminal enabling said gate when supplied with a comparator output; a comparator having first and second inputs, said first input being a manually selected numerically coded address, said second input being supplied with a numerical coded address representing a selected new time coded address signal, the output of said address comparator being applied to said terminal of said gate and enabling said gate when the numerical addresses in said comparator are in coincidence.
 9. In a signaling system having a central station and a plurality of remote stations, said central station having means for sequentially transmitting time coded address signals to each of said remote stations in a pre-established sequence, each of said remote stations transponding to said central station upon receipt of a respective time coded address signal, said time coded address comprising the combination including a fixed frequency signal having a duration T1 followed by a space having a duration T2, in turn followed by a fixed frequency signal having a duration T3, durations T1 and T2 being variable in accordance with a program to generate said time coded signals in said pre-established sequence, said duration T3 being constant, the combination comprising: a fixed frequency oscillator having a fixed frequency output; a gate having an output terminal and first and second input terminals, said fixed frequency output being applied to said first input terminal, said fixed frequency output being coupled to said remote stations through the output terminal of said gate when said gate is enabled, said gate being enabled when an enabling pulse is applied to said second terminal; first, second, third and fourth serially connected one-shot multivibrators, the trailing edge of the output pulse of each of said multivibrators triggering a succeeding multivibrator, the trailing edge of the output of said fourth multivibrator triggering said first multivibrator, each of said multivibrators having an R-C network, the duration of the output pulse of each multivibrator being a function of the parameters of a respective R-C network, the parameters of said third and fourth multivibrators being fixed, the parameters of said first and second one-shot multivibrators being sequentially alterable in accordance with said program, the duration of the outputs of said first, second, and third one-shot multivibrators being equal to T1, T2, and T3, respectively, the output of the fourth one-shot multivibrator having a fixed duration T4; a first plurality of duration determining means connectable into the R-C network of said first one-shot multivibrator for establishing the durations of the output pulses therefrom; a second plurality of duration determining means connectable into the R-C network of said second one-shot multivibrator for selectively re-establishing the durations of the output pulses therefrom; sequential switching means for sequentially connecting each of said duration determining means of said first and second pluralities into the R-C networks of said first and second one-shot multivibrators in accordance with said program, said sequential switching means being updated by said fourth one-shot multivibrator; a third and fourth plurality of selectable duration determining means; means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determining means of each of said third and fourth pluralities for re-establishing a selected new time coded address signal; means during the generation of the output pulse of said fourth one-shot multivibrator for displaying a received signal from a remote station; and means after receiving a signal from said remote station transponding to said selected new time coded address signal for continuing the operation of said sequential switching means.
 10. The invention as defined in claim 9 wherein said means for interrupting the updating of said sequential switching means and for substituting one of said selectable duration determining means comprises; a first normally closed switch for connecting the output from said second one-shot multivibrator to said sequential switching means for updating said sequential switching means; a second normally closed switch connecting sequentially selected ones of said first duration determining means into the R-C network of said first one-shot multivibrator; a third switch for connecting a selected one of said second plurality of duration determining means, said second switch being normally open; means for opening said first and second switches and for closing said third switch; and means for subsequently closing said first and second switches and for opening said third switch.
 11. The invention as defined in claim 10 wherein an addressed remote station transponds during the period of said update pulse; and means during the period of said update pulse for displaying a received signal from a remote station.
 12. The invention as defined in claim 11 wherein said means for displaying a received signal includes a gate having an output termianl and first and second input terminals, said first input terminal being supplied with decoded received signals, said second terminal enabling said gate when supplied with a comparator output; a comparator having first and second inputs, said first input being a manually selected numerically coded address, said second input being supplied with a numerically coded address representing a selected new time coded address signal, the output of said address comparator being applied to said terminal of said gate and enabling said gate when the numerical addresses in said comparator are in coincidence. 